Answer: 1. b
2. c
3. a
Explanation: A chemical reaction in equilibrium is actually in a dynamic euqilibrium, which means that changing a condition will make the equilibrium move to counteract the action and reestate the equilibrium.
For example, in the reaction:
N2(g) + 3H2(g) ⇄ 2NH3(g)
1. <u>Adding H2</u>: if you add the reagent, to reestate the equilibrium, the reaction will produce more products so, it will <u>move to the right</u>;
2. A <u>catalyst</u> doesn't interfere in the equilibrium, because it moves to the right and to the left at the same extent. Therefore, there is <u>no effect</u>.
3. <u>Decrease the pressure</u>: when you decrease the pressure of a reaction, the equilibrium will make the pressure increase again by moving towards the side of the reaction which has more molecules, so, it <u>shifts to the left</u>;